Producing solid products using powder products traditionally involves compressing the basic powder material in a die, said compression being obtained by means of punches sliding in said die, said die giving the finished solid product the required shape.
To meet the requirements of research and development, with the aim of perfecting presses that simulate industrial presses or for some specific applications, single-punch presses that operate slowly and use a small quantity of powder have been developed. Each of said punches, upper and lower respectively, is motorised, using a crank and rod member for example, so that the travel height of said punches, and in consequence, the compression rate, can be varied. In such facilities, the die is filled with powder by specific positioning of the lower die, and compression is obtained by actuating the upper punch so as to bring it down into said die.
Apart from the fact that employing a punch actuation system of this kind comes with a high level of inertia and a low speed relative to manufacturing machines, problems of reliability are also observed in terms of the cohesion of the resulting solid product, in so far as said product is frequently seen to burst, or to suffer from a lack of cohesion, translating into a return to powder form. In all cases, these presses are characterised by the fact that they simulate imperfectly, or even not at all, the phenomena occurring in industrial production presses.
Tablet manufacturing machines typically vary the translation height of the punches using a continuous system for rotating the punches using a turret and for compressing using rollers. This device is more difficult to use in R&D because of the minimum volume of powder needed and because of the mechanical stresses that this type of rotary press imposes on the tablet.
To dispense with these drawbacks, a first proposal has been made, for example in document FR-A-2 791 602, for a device that includes respective drive means for the upper and lower punches respectively, and that employs transmission means interposed kinetically between motor means and said punches, these transmission means each incorporating a cam. In so doing, the sinusoidal movement of prior art punches is eliminated by a linear movement that promotes the compression phase. Additionally, the use of cams allows the punch stroke rate to be modified in a straightforward manner as a function of the nature of the powder products used, thereby promoting device adaptability.
Another proposal has been made in document FR-A-2 855 094 for a development of this prior art. Said development comprises providing at least one of the two cams of the device previously described with a deformable external profile, intended to induce particular actions at least of the lower punch at the die, and particularly to promote the ejection of the product from the die after production. The compression rate of this system is then similar to that of industrial manufacturing presses.
Even if this development does unquestionably constitute a significant improvement relative to prior art devices, (extremely expensive hydraulic presses), it proves however to be complex to produce and expensive to manufacture.
The objective set by this invention is to propose a device of the type in question, which is both more straightforward, and therefore less expensive, to produce, and offers some reliability in terms of compression.
Additionally, it relates to a device for the manufacture of solid products that come in the form of multiple layer tablets for the purpose of perfecting the production lines of said solid products from powder materials.
The production of said multiple layer products is prone in fact to a certain number of problems, including the maintenance of the cohesion of each of the intermediate layers, the function of dosing by an adapted movement of the intermediate layers and the risk of the products constituting said layers getting mixed.
In fact, the devices known hitherto do not allow such multiple layer tablets to be produced reliably, in other words, without the risk of one, or even more, of the intermediate layers returning to the powder state, or while disregarding the proportioning/levelling function.